Physical vapor deposition (PVD) is a useful technique for producing thin films, enabling the fabrication of devices such as organic light emitting diodes (OLEDs) and photovoltaic devices (“solar cells”). Shadow masks are used to pattern the thin films during the deposition process. In general, there is a need for precision alignment between the various layers deposited in the fabrication of complex, layered structures such as OLEDs. Providing uniform tension in the shadow mask is an essential contributor to enabling precision alignment, especially in designs that use multiple shadow masks.
Existing methods for tensioning a shadow mask rely primarily on mechanisms in which clamp bars are affixed to the edges of the shadow mask and forces are applied to these clamp bars via pneumatic, hydraulic, or mechanical actuators. These existing methods for tensioning are difficult to control in a manner that results in uniform tension within the tensioned shadow mask. The portion of the mask which is in direct contact with the clamp bars cannot stretch, and therefore introduce non-uniformities in the mask tension. This is inherent in the use of clamping bars to tension the mask. Non-uniform tension leads to deformations within the mask, which contains a larger number of openings, often with very tight tolerances. The existing methods rely on mechanisms with moving parts, sometimes with complex controls, and are subject to a wide variety of failure mechanisms.
Thin film devices, such as OLED displays or photovoltaic cells, compete in the market with devices made using other technologies. In order to compete with other technologies, patterned thin film devices require more uniform and lower cost methods for tensioning shadow masks.